21.2 Overview of Lymphoid Structures PDF

21.2 Overview of Lymphoid Structures LEARNING OBJECTIVE 5. Name the two categories of lymphoid structures, and identify components of the body that belong to each category. The lymphatic system also is made up of specialized lymphoid (or lymphatic) structures. These structures include red bone marro...

21.2 Overview of Lymphoid Structures LEARNING OBJECTIVE 5. Name the two categories of lymphoid structures, and identify components of the body that belong to each category. The lymphatic system also is made up of specialized lymphoid (or lymphatic) structures. These structures include red bone marrow, the thymus, lymph nodes, the spleen, tonsils, lymphoid nodules, and mucosa-associated lymphoid tissue (MALT) (see lymphoid nodules not shown). figure 21.1; Lymphoid structures are categorized as either primary lymphoid structures or secondary lymphoid structures: Primary lymphoid structures are involved in the formation and maturation of lymphocytes. Both the red bone marrow and thymus are considered primary lymphoid structures. Secondary lymphoid structures are not involved in lymphocyte formation; instead, they house both lymphocytes and other immune cells following their formation. Secondary lymphoid structures are the sites where an immune response is initiated (see section 22.6). The major secondary lymphoid structures include the lymph nodes, spleen, tonsils, lymphoid nodules, and MALT. Each component is described in more detail in the next several sections and is summarized in table 21.1. Table 21.1 Lymphoid Structures Primary or Secondary Component Lymphoid Structures Location Function Red bone marrow Primary Spongy bone of selected Development of all bones formed elements; site of B-lymphocyte maturation Thymus Primary Superior mediastinum (in Site of T-lymphocyte adults); anterior and maturation and superior mediastinum (in differentiation children) Lymph nodes Spleen Secondary Secondary Along length of lymphatic Filter lymph; site where vessels; clusters in axillary, immune response is inguinal, and cervical initiated against a regions substance in the lymph Left upper quadrant of Filters blood; site where abdomen, near 9th–11th immune response is ribs, “wraps” partially initiated against a around stomach substance in the blood; removes aged erythrocytes and platelets; serves as erythrocyte and platelet reservoir Tonsils Lymphoid Secondary Secondary nodules Oral cavity and pharynx Protect against inhaled (throat) and ingested substances Every body organ and wall Protect body organs of appendix against foreign substances MALT (mucosa- Secondary Clusters of lymphoid Protects mucosal associated nodules within walls of membranes against lymphoid tissue) gastrointestinal (GI), foreign substances Primary or Secondary Component Lymphoid Structures Location Function respiratory, urinary, and reproductive tracts WHAT DID YOU LEARN? 5 How are primary lymphoid structures and secondary lymphoid structures differentiated? What are examples of each?